Milapse pointed me out to this image showing the part # from digikey that works perfectly as a male cable end for the K10D’s 8.3V DC input. So, a few parts later, and a couple of hours of soldering and testing, and I now have a power supply for the K10D that lets me hook up to:

12V Cigarette Lighter Plug

12V AC->DC adapter

Any one of my 12V SLA batteries

Note: The K10D and K20D share the same AC adapter (D-AC50), so this design will work for both cameras.

All can be done for less than the price of the standard Pentax D-AC50 AC adapter, and a few hours of sweating over a hot iron =) Namely, I can now run the camera from the same 8Ah battery I run the TLA from, meaning I only have to charge one battery out in the field! (Try getting enough engine time to charge the big SLA, three NiMH’s, a laptop, etc..) And, you know, I can run it on AC inside of the studio!